Traditionally, two types of surgical procedures have been used to repair injured connective tissue. In the first, a naturally occurring tissue is used as the basis for the graft, and in the second, a synthetic material is used. When a naturally occurring tissue is grafted, it is often one that is harvested from the injured patient (i.e., an autograft), but the extent to which autografts may be made is limited by the amount of tissue available. In addition, donor site morbidity and necrosis of the implanted graft are problems that have not yet been overcome. As alternatives, one can graft allogenic tissue (i.e., tissue taken from an individual of the same species as the recipient but with different hereditary factors) or xenogenic tissue (i.e. tissue taken from a donor who is not of the same species as the recipient). Use of these tissue types eliminates the problems associated with harvesting tissue from the injured patient, but there may be a risk that the graft will transmit disease. The injured patient may also mount an immune response that leads to graft rejection. Thus, allogenic and xenogenic tissues are used in only a limited number of reconstructive surgeries.
While synthetic materials and devices are not as susceptible to acute rejection, they have generally failed to show successful long-tern results. For example, devices used for the replacement of ligaments commonly fail over a 2–10 year period due to synovitis, loosening, or implant failure. Following implantation, continuous loading of the device and abrasion against joint tissues causes wear, creep, and fatigue, which worsen until the device eventually fails.
Some synthetic devices have been designed to encourage tissue ingrowth, as it was thought that this would strengthen the device. Unfortunately, the ingrowth observed has been disorganized and not of a sufficient quality or quantity to lend the anticipated benefit
In addition to the traditional surgical approaches discussed above, tissues have been repaired by tissue engineering, which is a multidisciplinary science that utilize principles from the life sciences, engineering, and other disciplines to create cellular constructs for transplantation. These constructs are generally created in vitro. However, in some circumstances, they are also created in vivo, where the body is effectively used as a bioreactor. When this is done, the constructs are seeded with cells, such as mesenchymal cells, either before or after they are implanted (see, e.g., U.S. Pat. No. 5,855,610). Ibarra et al. (see “Transplantation of Tissue Engineered Meniscus in Sheep”, 44th Meeting, Orthopaedic Research Society, March 16–19, New Orleans, La., USA) also report a method involving implantation of a scaffold with a view to generating a tissue-engineered implant. This method also comprises the step of seeding the scaffold with cells prior to implantation.